A wireless base station or cell site is typically the dominate power consumer for many wireless carriers. Therefore, decreasing the energy used in wireless base stations is important to reducing the energy usage associated with wireless carriers. Cooling the equipment is usually one of the areas of higher energy usage at a cell site. Accordingly, any improvement that reduces energy usage has the additional benefit of reduced cooling expense. Much of the work to date has been focused on individual efforts to improve the efficiency of the components of the system such as the rectifiers, power amplifiers, cooling system, etc.
The service providers require the base station to operate and provide service continuously even during extreme weather conditions and periods of primary power outages. To provide uninterrupted service during power outages a power back-up scheme is required. The requirements vary but it is not unusual to have the back-up system being designed to supply full power for 8 hours or more. Although the loads are generally small, typically less than 15 kW, battery back-up alone may not be practical due to space requirements. Therefore many of the systems use a diesel generator or, more increasingly, fuel cells to provide the long term back-up while the batteries supply the load during transitions. The batteries are connected across the DC bus feeding the load and the bus voltage is maintained by the rectifiers at the float voltage of the batteries, typically 54.5 V or 27.75 V for valve regulated batteries. This ensures the batteries are charged and available to provide the required reserve time during the transition to reserve power.
The power system itself consists of rectifiers which receive an AC input, typically from an electric utility, and convert it to the DC bus voltage. A system controller is also provided which controls the operation of the rectifiers and monitors the power system operation. Some attempts to improve the efficiency of the power system have centered on improving the efficiency of the rectifiers including the light load efficiency, and utilizing the system controller to monitor the bus current and configure the rectifiers to minimize losses.